I have just got the Dual GPS.
It works OK, and the free phone shop app shows the satellite details too.
But there is no way, in the Ipad2, to select which GPS to use. I have so far only tried it with Memory Map and it appears that if the external GPS dies, the app just quietly stops working, or quietly switches over to the built-in GPS - with its reliability issues.
I don't know if other GPS apps on IOS have an explicit config for which GPS to use, but I have never seen this. It's really crap.
The only solution is to put the Ipad into Airplane mode, when the internal GPS is disabled.
The other thing I noticed that when the GPS battery goes flat, the MM app just sits there, showing the last position. No message, no warning...